Method of processing data of optical mouse

ABSTRACT

Disclosed herein is a method of processing data of an optical mouse. The method includes the steps of calculating a motion vector of the optical mouse through processing of digitally converted image pixel data in an Image Signal Processor (ISP) by sequentially overlapping a reference image of an n−1 th frame to a present image of an nth frame and determining a moving direction of the optical mouse using approximately equal parts in the reference and present images; and transmitting the calculated motion vector to a personal computer through an interface; wherein the ISP includes an X axis navigation engine for processing data on a reference image for the motion of an X axis direction among the processed image pixel data and a Y axis navigation engine for processing data on a reference image for the motion of a Y axis direction among the processed image pixel data.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a method of processing imagedata of an optical mouse, and more particularly, to a method ofprocessing image data of an optical mouse, which is capable of improvingthe detection of the two-dimensional motion of an optical mouse.

2. Description of the Prior Art

FIG. 1 is a block diagram showing the processing of image data of ageneral optical mouse. As shown in FIG. 1, the data process block of thegeneral optical mouse includes an analog process unit 10 that reads theimage of a surface under the optical mouse in analog data and convertsthe analog data into digital data, and a digital process unit 20 thatcalculates and outputs a motion vector with respect to time using thedigital data.

The analog process unit 10 includes an image pixel array 12 thatgenerates an analog image according to the amount and intensity of lightreflected by a surface under the optical mouse, and an Analog-to-DigitalConverter (ADC) 14 that converts the analog data of the image pixelarray 12 into the digital data.

Additionally, the digital process unit 20 includes an Image SignalProcessor (ISP) 22 that calculates a motion vector by processing thedigital data, and a Personal Computer (PC) interface 24 that receivesdata output from the image signal processor 22 and transmits data to theimage signal processor 22 through data communication.

There is described an algorithm for processing image data of an opticalmouse to calculate the motion vector of the optical mouse through theimage signal processor 22 with reference to FIG. 2. FIG. 2 is aschematic view illustrating a conventional method of processing imagedata of an optical mouse.

To implement the algorithm, at least three memory spaces are needed tostore pixel data. The memory spaces store the reference image of an n−1th frame for an X axis and a Y axis, the present image of an nth framefor the X axis and the Y axis, and the reference image of the nth framefor the X axis and the Y axis.

First, the reference image of the n−1 th frame is selectively extractedfrom the total image of the n−1 th frame in order to find the motion ofthe optical mouse in the nth frame. The present image of the nth frameis the total image of the nth frame. Last, the reference image of thenth frame is selectively extracted from the present image of the nthframe and become a reference image to find the motion of the opticalmouse in an n+1 th frame.

As described above, the moving direction of the motion vector isdetermined using most approximately equal parts of the reference imageof the n−1 th frame and the present image of the nth frame while thereference image of the n−1 th frame is sequentially overlapped with thepresent image of the nth frame. The reference and present images shouldideally coincide with each other by 100%, but the reference and presentimages does not actually coincide with each other by 100% due to thenoise of the images and so on in terms of characteristics of an imagesensor.

The motion of the optical mouse is found through repeated performance ofthe above-described process.

There are matters to be considered in the repeated performance of theprocess. For one, detection errors of one pixel or less always exist inthe algorithm for calculating the motion vector of the optical mousebecause the image sensor has a physical size. If the reference image ofthe n−1 th frame is updated to the reference image of the nth frame inevery frame, the motion of the optical mouse cannot be detected when theoptical mouse is slowly moved by one pixel or less. To solve thisproblem, if the reference image of the n−1 th frame is updated only whenmotion is detected instead of updating the reference image of the n−1 thframe in every frame, the detection errors can be minimized and themotion of the optical mouse can be detected for the case where theoptical mouse is slowly moved by one pixel or less.

FIG. 3 is a view illustrating the optimal division of a conventionalnavigation engine using one channel, which shows a case where aone-channel algorithm is applied. In the case of applying theone-channel algorithm, if the optical mouse moves 0.5 pixel in the Xaxis direction and 0.2 pixel in the Y axis direction in every frame, forexample, at an interval of 588 μs, respectively, the motion of one pixelor less cannot be detected.

In this case, there is described the motion of the optical mouse rangingfrom a first frame to a sixth frame with reference to FIG. 3, as anexample.

Referring to the motion of the optical mouse with respect to time in apresent nth frame, if the amounts of motions in the X and Y axisdirections are 0 and 0 in the first frame (588 μs*1), respectively, theamounts of the motions in the X and Y axis directions are 0.5 and 0.2 inthe second frame (588 μs*2), respectively, the amounts of the motions inthe X and Y axis directions are 1 and 0.4 in the third frame (588 μs*3),respectively, the amounts of the motions in the X and Y axis directionsare 1.5 and 0.6 in the fourth frame (588 μs*4), respectively, theamounts of the motions in the X and Y axis directions are 2 and 0.8 inthe fifth frame (588 μs*5), respectively, and the amounts of the motionsin the X and Y axis directions are 2.5 and 1 in the sixth frame (588μs*6), respectively. As in the above-described method, if the motion ofthe optical mouse occurs in an eleventh frame, the actual amounts of themotions in the X and Y axis directions are 5 and 2, respectively, butthe detected amounts of the motions in the X and Y axis directions are 5and 0, respectively.

In this case, VX and VY, which are the sum of vectors accumulated in theX axis direction and the sum of vectors accumulated in the Y axisdirection, respectively, are represented as the XY coordinates (0, 0) inthe second frame in the case where the optical mouse moves 0.5 pixel inthe X axis direction and 0.2 pixel in the Y axis direction, compared tothe motion of the first frame. The reason is that the motion of onepixel or less cannot be detected when the second frame is compared tothe reference image of the n−1 th frame, for example, the first frame.Next, the VX and VY are represented as XY coordinates (1, 0) in thethird frame in the case where the optical mouse moves 0.5 pixels in theX axis direction and 0.2 pixel in the Y axis direction, compared to themotion of the second frame. 0.5 pixel is accumulated in the X axisdirection in each of the second and third frames from the referenceimage of the n−1 th frame, and the amount of the motion in the X axisdirection therefore becomes 1; while 0.2 pixel is accumulated in the Yaxis direction in each of the second and third frames from the referenceimage of the n−1 th frame, and the amount of motion in the Y axisdirection therefore becomes 0.4. Accordingly, motion of one pixel orless cannot be detected, so the value of VY becomes 0. Thereafter, thereference image of the n−1 th frame is updated to the third framebecause the value of the VX is changed from 0 to 1.

Accordingly, the motion in only the X axis direction can be detectedwhen the motion of the optical mouse occurs in the eleventh frame, sothe values of the VX and the VY are 5 and 0, respectively. However, themotion in the Y axis direction cannot be detected in the case where theoptical mouse moves 0.2 pixel in the Y axis direction in every frame, sothe value of the VY becomes 0 although the optical mouse actually moves2 pixels in the Y axis direction.

In short, the XY coordinates of VX and VY, which are the sum of vectorsaccumulated in the X axis direction and the sum of vectors accumulatedin the Y axis direction, respectively, are represented as (2, 0) by thecalculation of (0, 0)+(1, 0)+(0, 0)+(1, 0)+(0, 0). Accordingly, althoughthe actual amounts of the motions in the X and Y axis directions are 2.5and 1 in the sixth frame, respectively, the value of the VY is notdetected as “1”. The detection error of the amount of the motion in theX axis is 0.5 by the calculation of 2.5−2 and the detection error of 0.5is detected in the next frame, that is, a seventh frame. In the casewhere the motion of the optical mouse occurs in the eleventh frame, theactual amounts of the motions in the X and Y axis directions, are 5 and2, respectively however, the detected amounts of the motions in the Xand Y axis directions, are 5 and 0, respectively. That is, the motion inthe X axis direction can be detected, and the motion in the Y axisdirection cannot be precisely detected.

In the application of the conventional method of processing image dataof the optical mouse, the two-dimensional motion of an optical mouseshould be corrected.

That is, if the two-dimensional motion is calculated using a singlenavigation engine, for example, an algorithm for processing image data,the detection errors of the motion are increased according to conditionsunder which a reference image is updated. For example, if the conditionis set to a case where the motion in the X axis direction or the motionin the Y axis direction is detected, the motion in the Y axis directionis not detected when the motion in the X axis direction is greater thanone pixel and the motion in the Y axis direction is equal to or lessthan one pixel. For another case, if the condition is set to a casewhere the motion in the X axis direction and the motion in the Y axisdirection are detected, the reference image is not updated until themotion in the X axis direction and the motion in the Y axis directionare detected at the same time, so the detection errors of the motion areincreased.

Accordingly, if the two-dimensional motion of the optical mouse iscalculated using the single navigation engine for processing image dataof the conventional optical mouse, the detection of the small motion ofone pixel or less of the optical mouse in one direction, for example,the X axis direction or Y axis direction, is actually improved, but thedetection of the motion of the optical mouse in the other direction canbe deteriorated.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind theabove problems occurring in the prior art, and an object of the presentinvention is to provide a method of processing image data of an opticalmouse, in which navigation engines are individually used to detectmotions in X and Y axis directions, respectively, not but using a singlenavigation engine to detect two-dimensional motion, thereby improvingthe detection of the optical mouse in X and Y axis directions.

In order to accomplish the above object, the present invention providesa method of processing data of an optical mouse, including calculating amotion vector of the optical mouse through processing of digitallyconverted image pixel data in an ISP by sequentially overlapping areference image of an n−1 th frame to a present image of an nth frameand determining a moving direction of the optical mouse using mostapproximately equal parts in the reference and present images; andtransmitting the calculated motion vector to a personal computer throughan interface; wherein the ISP includes an X axis navigation engine forprocessing data on a reference image for the motion of an X axisdirection among the processed image pixel data and a Y axis navigationengine for processing data on a reference image for the motion of a Yaxis direction among the processed image pixel data, and the X and Yaxis navigation engines each store the reference image of the n−1 thframe, the present image of the nth frame, and a reference image of thenth frame.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a block diagram showing the processing of image data of ageneral optical mouse;

FIG. 2 is a schematic view illustrating a conventional method ofprocessing image data of an optical mouse;

FIG. 3 is a view illustrating the optimal division of a conventionalnavigation engine using one channel;

FIG. 4 illustrates the operation of an algorithm for processing imagedata in an optical mouse in accordance with the present invention;

FIG. 5 illustrates the sum of vectors obtained by X and Y axisnavigation engines;

FIG. 6 is a view illustrating the optimal division of navigation enginesusing two channels in accordance with the present invention; and

FIG. 7 is a flowchart of the algorithm for processing image data of twochannels using optimally divided navigation engines.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference now should be made to the drawings, in which the samereference numerals are used throughout the different drawings todesignate the same or similar components.

Hereinafter, there is described a preferred embodiment of the presentinvention with reference to the accompanying drawings.

FIG. 4 illustrates the operation of an algorithm for processing imagedata in an optical mouse in accordance with the present invention.

In the present invention, two navigation engines for detecting motionsin X and Y axis directions, respectively, are provided to minimize thedetection errors of the two-dimensional motion of the optical mouse.FIG. 5 illustrates the sum of vectors obtained by X and Y axisnavigation engines. Referring to FIG. 5, a motion calculated in an Xaxis navigation engine is represented by a vector {right arrow over(X)}, a motion calculated in a Y axis navigation engine is representedby a vector {right arrow over (Y)}, the two-dimensional motion vector{right arrow over (Z)} of the optical mouse is calculated by the sum ofthe vectors {right arrow over (X)} and {right arrow over (Y)}, that is,{right arrow over (Z)}={right arrow over (X)}+{right arrow over (Y)}.

An advantage of the present invention is that it obtains the precisevalue of the two-dimensional motion vector of the optical mouse movingalong a slanting line, a circle, or the like. Accordingly, a motionsimilar to the actual motion of the optical mouse can be found.

The concept of the division of a navigation engine can be extended todimensions other than one dimension, for example, two dimensions orthree dimensions.

Further, the preferred embodiment of the present invention can becomeapparent through the description of a case where the algorithm using twochannels is applied. In this case, the channel is defined as adimension, so one channel represents one direction, such as an X axisdirection or Y axis direction (the one dimension), and two channelsrepresents two directions, such as the X and Y axis directions (the twodimensions).

FIG. 6 is a view illustrating the optimal division of navigation enginesusing two channels in accordance with the present invention, which showsa case where a two-channel algorithm is applied.

In the case of applying the two-channel algorithm, if the optical mousemoves 0.5 pixel in the X axis direction and 0.2 pixel in the Y axisdirection in every frame, for example, at an interval of 588 μs,respectively, the motion of one pixel or less cannot be detected, as inthe one-channel algorithm.

In this case, there is described the motion of the optical mouse rangingfrom a first frame to a sixth frame with reference to FIG. 6, as anexample.

Referring to the motion of the optical mouse with respect to time in apresent nth frame, if the amounts of motions in the X and Y axisdirections are 0 and 0 in the first frame (588 μs*1), respectively, theamounts of the motions in the X and Y axis directions are 0.5 and 0.2 inthe second frame (588 μs*2), respectively, the amounts of the motions inthe X and Y axis directions are 1 and 0.4 in the third frame (588 μs*3),respectively, the amounts of the motions in the X and Y axis directionsare 1.5 and 0.6 in the fourth frame (588 μs*4), respectively, theamounts of the motions in the X and Y axis directions are 2 and 0.8 inthe fifth frame (588 μs*5), respectively, and the amounts of the motionsin the X and Y axis directions are 2.5 and 1 in the sixth frame (588μs*6), respectively. As in the above-described method, the actualamounts of the motions in the X and Y axis directions are 5 and 2,respectively, if the motion of the optical mouse occurs in an eleventhframe.

In this case, the value of VX, that is, the vector {right arrow over(X)}, which is the sum of vectors accumulated in the X axis direction isrepresented as 0 in the first and second frames. The reason is that themotion of one pixel or less in the X axis direction cannot be detectedin either of the first and second frames. Next, the value of the VX isrepresented as 1 in the third frame because the optical mouse moves onepixel in the X axis direction. Additionally, the amount of the motion inthe X axis direction is determined as a certain value, not but 0, so thereference image of an n−1 th frame is updated to the reference image ofthe nth frame. Accordingly, if the motion of the optical mouse occurs inan eleventh frame, the value of the VX is represented as 5 because themotion in the X axis direction is only detected.

Meanwhile, the value of VY, that is, the vector {right arrow over (Y)},which is the sum of vectors accumulated in the Y axis direction, isrepresented as 0 in the first and second frames. The reason is thatmotion of one pixel or less in the Y axis direction cannot be detectedin either of the first and second frames. Next, the value of the VY isrepresented as 0 in the third frame to the fifth frame because theoptical mouse moves one pixel or less in the Y axis direction. Next, thevalue of the VY is represented as 1 in the sixth frame because theoptical mouse moves one pixel in the Y axis direction. Additionally, thereference image of the n−1 th frame is updated to the reference image ofthe nth frame. The above-described processes are applied to the eleventhframe.

In short, the value of the VX, which is the sum of vectors accumulatedin the X axis direction, is 2 by the calculation of 0+1+0+1+0, and thevalue of the VY, which is the sum of the vectors accumulated in the Yaxis direction, is 1 by the calculation of 0+0+0+0+1. Accordingly, theaccumulated sums of the vectors VX and VY can be represented as the XYcoordinates (2, 1), and the actual amounts of the motions in the X and Yaxis directions are represented as the XY coordinates (2.5, 1) in thesixth frame. The detection error of the amount of the motion in the Xaxis is 0.5 by the calculation of 2.5−2 and the detection error of 0.5is detected in the next frame, that is, a seventh frame. In the casewhere the motion of the optical mouse occurs in the eleventh frame, theactual amounts of the motions in the X and Y axis directions, are 5 and2, respectively, and detected amounts of the motions in the X and Y axisdirections, are also 5 and 2, respectively. That is, the motion in the Xaxis direction can be detected, and the motion in the Y axis directioncannot be precisely detected.

Next, there is described the two-channel algorithm for the X and Y axisdirections with reference to FIG. 7.

FIG. 7 is a flowchart of the algorithm for processing image data of twochannels using optimally divided navigation engines.

Image data digitally converted from analog data detected in an imagepixel array is input at step S11. The input image data is stored in thepresent buffer of an nth frame as the present image of the nth frame atstep S12. Additionally, some images are extracted from the presentbuffer of the nth frame and the extracted images are stored in thereference buffer of the nth frame at step S13.

Thereafter, the stored present image of the nth frame is compared to thereference image of an n−1 th X frame, which is an n−1 th frame of the Xaxis direction, and the reference image of an n−1 th Y frame, which isan n−1 th frame of the Y axis direction, at step S14. Thereafter, VX,which is the vector of the X axis direction, is calculated usingapproximately equal parts obtained by comparing the present image of thenth frame and the reference image of the n−1 th X frame, and VY, whichis the vector of the Y axis direction, is calculated using approximatelyequal parts by comparing the present image of the nth frame and thereference image of the n−1 th Y frame at step S15.

If the value of the calculated VX is not “0”, the reference image of then−1 th X frame is updated to the reference image of the nth frame, whileif the value of the calculated VX is “0”, the reference image of the n−1th X frame is maintained; while if the value of the calculated VY is not“0”, the reference image of the n−1 th Y frame is updated to thereference image of the nth frame, while if the value of the calculatedVY is “0”, the reference image of the n−1 th Y frame is maintained atstep S16. Thereafter, a motion vector is obtained by adding thecalculated vectors VX and VY at step S17.

It is preferable that the number of the reference image of the n−1 thframe is N (N=1˜3), and the number of present and reference images ofthe nth frame is each one. N=1 means one dimension. N=2 means twodimensions. N=3 means three dimensions.

As described above, in the present invention, the motion vector isobtained by adding the vectors VX and VY calculated by independentnavigation engines of the X and Y axis directions instead of onenavigation engine using one channel, so the natural two-dimensionalmotion of the optical mouse can be represented.

As described above, the present invention, provides a method ofprocessing image data of an optical mouse, in which image data outputfrom the image pixel array of an integrated circuit for the opticalmouse is converted into digital image data, and the motion vector iscalculated by adding VX and VY obtained by the application of anavigation algorithm in each of the X and Y axis directions so as toobtain the change of the location of the image data by providing theconverted digital image data to the navigation algorithm, therebyimproving the detection of the two-dimensional motion of the opticalmouse.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. A method of processing data of an optical mouse, comprising:calculating a motion vector of the optical mouse through processing ofdigitally converted image pixel data in an Image Signal Processor (ISP)by sequentially overlapping a reference image of an n−1 th frame to apresent image of an nth frame and determining the most approximatelyequal parts in the reference and present images as a moving direction ofthe optical mouse; and transmitting the calculated motion vector to apersonal computer through an interface; wherein the ISP includes an Xaxis navigation engine for processing data on a reference image for themotion of an X axis direction among the processed image pixel data and aY axis navigation engine for processing data on a reference image forthe motion of a Y axis direction among the processed image pixel data,and the X and Y axis navigation engines each store the reference imageof the n−1 th frame, the present image of the nth frame, and a referenceimage of the nth frame.
 2. The method according to claim 1, wherein themotion vector {right arrow over (Z)} of the optical mouse is determinedby adding the motion represented as {right arrow over (X)} calculated bythe X axis navigation engine to the motion represented as {right arrowover (Y)} calculated by the Y axis navigation engine, that is, {rightarrow over (Z)}={right arrow over (X)}+{right arrow over (Y)}.
 3. Themethod according to claim 1, wherein a number of the reference image ofthe n−1 th frame is N (N=1˜3), and a number of present and referenceimages of the nth frame is each one.
 4. The method according to claim 1,wherein the step of calculating a motion vector comprises the steps of:storing the digitally converted image pixel data in a present buffer ofthe nth frame as the present image of the nth frame; extracting someimages from the present buffer of the nth frame and storing theextracted images in a reference buffer of the nth frame; comparing thestored present image of the nth frame with the reference image of then−1 th frame of the X axis direction and the reference image of the n−1th frame of the Y axis direction; calculating VX, which is a vector ofthe X axis direction, using approximately equal parts in the presentimage of the nth frame and the reference image of the n−1 th frame ofthe X axis direction by comparing the present and reference images, andcalculating VY, which is a vector of the Y axis direction, usingapproximately equal parts in the present image of the nth frame and thereference image of the n−1 th frame of the Y axis direction by comparingthe present and reference images; and calculating the motion vector byadding the calculated vectors VX and VY.
 5. The method according toclaim 4, wherein if a value of the calculated VX is not “0”, thereference image of the n−1 th frame of the X axis direction is updatedto the reference image of the nth frame, while if the value of thecalculated VX is “0”, the reference image of the n−1 th frame of the Xaxis direction is maintained; while if a value of the calculated VY isnot “0”, the reference image of the n−1 th frame of the Y axis directionis updated to the reference image of the nth frame, while if the valueof the calculated VY is “0”, the reference image of the n−1 th frame ofthe Y axis direction is maintained.
 6. A method of processing digitallyconverted image pixel data of an Image Signal Processor (ISP) includedin an optical mouse, comprising: calculating vectors VX and VY using Xaxis and Y axis navigation engines for processing motions in X and Yaxis directions, respectively; and calculating a motion vector of theoptical mouse by adding the calculated vectors VX and VY.
 7. The methodaccording to claim 6, wherein the step of calculating the vector VXcomprises; storing the digitally converted image pixel data in a presentbuffer of an nth frame as a present image of an nth frame; extractingsome images from the present buffer of the nth frame and storing theextracted images in a reference buffer of the nth frame; comparing thepresent image of the nth frame with a reference image of an n−1 th frameof the X axis direction; and calculating VX, which is a vector of the Xaxis direction, using approximately equal parts in the present andreference images by comparing the present and reference images.
 8. Themethod according to claim 6, wherein the step of calculating the vectorVY comprises; storing the digitally converted image pixel data in apresent buffer of an nth frame as a present image of an nth frame;extracting some images from the present buffer of the nth frame andstoring the extracted images in a reference buffer of the nth frame;comparing the present image of the nth frame with a reference image ofan n−1 th frame of the Y axis direction; and calculating VY, which is avector of the Y axis direction, using approximately equal parts in thepresent and reference images by comparing the present and referenceimages.
 9. A method of processing data of an optical mouse, comprising:analyzing optical data in an Image Signal Processor (ISP) wherein theISP includes an X axis navigation engine for processing data on areference image for the motion of an X axis direction among theprocessed image pixel data and a Y axis navigation engine for processingdata on a reference image for the motion of a Y axis direction among theprocessed image pixel data, and the X and Y axis navigation engines eachstore the reference image of the n−1 th frame, the present image of thenth frame, and a reference image of the nth frame; calculating a vectorVX in the X-axis direction using approximately equal parts in thepresent image of the nth frame and the reference image of the n−1 thframe of the X axis direction by comparing the present and referenceimages; calculating a vector VY in the Y axis direction, usingapproximately equal parts in the present image of the nth frame and thereference image of the n−1 th frame of the Y axis direction by comparingthe present and reference images; calculating a motion vector by addingthe calculated vectors VX and VY, wherein if a value of the calculatedVX is not “0”, the reference image of the n−1 th frame of the X axisdirection is updated to the reference image of the nth frame; wherein ifthe value of the calculated VX is “0”, the reference image of the n−1 thframe of the X axis direction is maintained; wherein if a value of thecalculated VY is not “0”, the reference image of the n−1 th frame of theY axis direction is updated to the reference image of the nth frame;wherein if the value of the calculated VY is “0”, the reference image ofthe n−1 th frame of the Y axis direction is maintained; and transmittingthe calculated motion vector to a personal computer through aninterface.
 10. The method according to claim 9, wherein a number of thereference image of the n−1 th frame is N (N=1˜3), and a number ofpresent and reference images of the nth frame is one.
 11. A method ofprocessing digitally converted image pixel data of an Image SignalProcessor (ISP) included in an optical mouse, comprising: a. calculatingvectors VX and VY using X axis and Y axis navigation engines forprocessing motions in X and Y axis directions, respectively; and b.calculating a motion vector of the optical mouse by the steps of (1)storing the digitally converted image pixel data in a present buffer ofthe nth frame as the present image of the nth frame; (2) extracting someimages from the present buffer of the nth frame and storing theextracted images in a reference buffer of the nth frame; (3) comparingthe stored present image of the nth frame with the reference image ofthe n−1 th frame of the X axis direction and the reference image of then−1 th frame of the Y axis direction; (3) calculating VX, which is avector of the X axis direction, using approximately equal parts in thepresent image of the nth frame and the reference image of the n−1 thframe of the X axis direction by comparing the present and referenceimages, and calculating VY, which is a vector of the Y axis direction,using approximately equal parts in the present image of the nth frameand the reference image of the n−1 th frame of the Y axis direction bycomparing the present and reference images; and (4) calculating themotion vector by adding the calculated vectors VX and VY; wherein if avalue of the calculated VX is not “0”,the reference image of the n−1 thframe of the X axis direction is updated to the reference image of thenth frame, while if the value of the calculated VX is “0”,the referenceimage of the n−1 th frame of the X axis direction is maintained; whileif a value of the calculated VY is not “0”, the reference image of then−1 th frame of the Y axis direction is updated to the reference imageof the nth frame, while if the value of the calculated VY is “0”, thereference image of the n−1 th frame of the Y axis direction ismaintained.
 12. The method according to claim 11, wherein the step ofcalculating the vector VX comprises; storing the digitally convertedimage pixel data in a present buffer of an nth frame as a present imageof an nth frame; extracting some images from the present buffer of thenth frame and storing the extracted images in a reference buffer of thenth frame; comparing the present image of the nth frame with a referenceimage of an n−1 th frame of the X axis direction; and calculating VX,which is a vector of the X axis direction, using approximately equalparts in the present and reference images by comparing the present andreference images.
 13. The method according to claim 11, wherein the stepof calculating the vector VY comprises; storing the digitally convertedimage pixel data in a present buffer of an nth frame as a present imageof an nth frame; extracting some images from the present buffer of thenth frame and storing the extracted images in a reference buffer of thenth frame; comparing the present image of the nth frame with a referenceimage of an n−1 th frame of the Y axis direction; and calculating VY,which is a vector of the Y axis direction, using approximately equalparts in the present and reference images by comparing the present andreference images.